Home battery and inverter size: critical loads or whole house?
Start with a preset or tick your own loads, set how long the outage should be covered, and see the battery energy, the inverter power and how the load spreads across the two 120 V legs of a US split-phase home. Wattages are typical values for each kind of appliance, not measurements; check your labels.
How this is worked out
- Energy: for each load, watts x share of time it actually runs x hours switched on per day, scaled to the outage length. Usable kWh is divided by 90% depth of discharge (typical for LFP home batteries) to get the nominal size.
- Continuous inverter: sum of running watts plus 25% headroom. Surge: running watts plus only the single largest start-up extra (start minus running), since motors rarely start together.
- Split phase: 120 V loads are placed biggest first on the lighter leg; a 240 V load draws its watts / 240 A on both legs. Units usually share their rating across the two legs, so one overloaded leg can trip a unit that looks big enough on paper.
- Whole-house here means the common appliances in our typical list, not a measured house. A real whole-house size comes from a service load calculation by an electrician.